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Abstract:
The thermoelectric properties of single-crystalline and polycrystalline
FeGa 3 are systematically investigated over a wide temperature range. At
low temperatures, below 20 K, previously not known pronounced peaks in
the thermal conductivity (400-800WK -1 m -1) with corresponding maxima
in the thermopower (in the order of -16000muV K -1) were found in
single-crystalline samples. Measurements in single crystals along [100]
and [001] directions indicate only a slight anisotropy in both the
electrical and thermal transports. From susceptibility and heat-capacity
measurements, a magnetic or structural phase transition was excluded.
Using density functional theory based calculations, we have revisited
the electronic structure of FeGa 3 and compared the magnetic (including
correlations) and nonmagnetic electronic densities of states.
Thermopower at fixed carrier concentrations is calculated using
semiclassical Boltzmann transport theory, and the calculated results
match fairly with our experimental data. The inclusion of strong
electron correlations treated in a mean field manner (by LSDA + U) does
not improve this comparison, rendering strong correlations as the sole
explanation for the low-temperature enhancement unlikely. Eventually,
after a careful review, we assign the peaks in the thermopower as a
manifestation of the phonon-drag effect, which is supported by
thermopower measurements in a magnetic field.
